Filtering ActiveRecord queries in rails

Question

I'm used to Django where you can run multiple filter methods on querysets, ie Item.all.filter(foo="bar").filter(something="else").

The however this is not so easy to do in Rails. Item.find(:all, :conditions => ["foo = :foo", { :foo = bar }]) returns an array meaning this will not work:

Item.find(:all, :conditions => ["foo = :foo", { :foo = 'bar' }]).find(:all, :conditions => ["something = :something", { :something = 'else' }])

So I figured the best way to "stack" filters is to modify the conditions array and then run the query.

So I came up with this function:

 def combine(array1,array2)
   conditions = []
   conditions[0] = (array1[0]+" AND "+array2[0]).to_s
   conditions[1] = {}
   conditions[1].merge!(array1[1])
   conditions[1].merge!(array2[1])
   return conditions
 end

Usage:

array1 = ["foo = :foo", { :foo = 'bar' }] array2 = ["something = :something", { :something = 'else' }] conditions = combine(array1,array2) items = Item.find(:all, :conditions => conditions)

This has worked pretty well. However I want to be able to combine an arbitrary number of arrays, or basically shorthand for writing:

conditions = combine(combine(array1,array2),array3)

Can anyone help with this? Thanks in advance.

Answer 1

You can take a look at Searchlogic.
It makes it easier to use conditions on ActiveRecord sets, and even on Arrays.

Hope it helps.

Answer 2

I think what you want is this: Named Scope

Answer 3

You can (or at least used to be able to) filter like so in Rails:

find(:all, :conditions => { :foo => 'foo', :bar => 'bar' })

where :foo and :bar are field names in the active record. Seems like all you need to do is pass in a hash of :field_name => value pairs.

Answer 4

I wouldn't do it like you proposed.

Since find return an array, you can use array methods to filter it, on example:

Item.find(:all).select {|i| i.foo == bar }.select {|i| i.whatever > 23 }...

You can also achive what you want with named scopes.

Answer 5

What you want are named scopes:

class Item < ActiveRecord::Base
  named_scope :by_author, lambda {|author| {:conditions => {:author_id => author.id}}}
  named_scope :since, lambda {|timestamp| {:conditions => {:created_at => (timestamp .. Time.now.utc)}}}
  named_scope :archived, :conditions => "archived_at IS NOT NULL"
  named_scope :active, :conditions => {:archived_at => nil}
end

In your controllers, use like this:

class ItemsController < ApplicationController
  def index
    @items = Item.by_author(current_user).since(2.weeks.ago)
    @items = params[:archived] == "1" ? @items.archived : @items.active
  end
end

The returned object is a proxy and the SQL query will not be run until you actually start doing something real with the collection, such as iterating (for display) or when you call Enumerable methods on the proxy.